Rotary screw machine

ABSTRACT

A rotary screw machine in which the openings for charging and discharging a gaseous working medium are located in the casing at both faces of the screws, and in which, in each portion of the casing adjacent to the like faces of the screws at a certain distance from the opening provided in this portion of the casing, a groove is provided along the line of engagement of the teeth of the screws and facing the adjacent faces of the screws. One end of this groove is located at the dedendum circle of the teeth of the female screw while the other end of the groove is located beyond the addendum circle of the teeth of this screw.

I United States Patent lnventors U.S.S.R. App1.No. 18,167 Filed Mar. 10,1970 Patented Oct. 5, 1971 ROTARY SCREW MACHINE 3 Claims, 5 DrawingFigs.

US. Cl 418/189, 418/190, 418/201 Int. Cl F01c 21/00, F01c 1116 FieldofSearch 418/189,

Primary Examiner-Carlton R. Croyle Assistant Examiner-Wilbur J. GoodlinAttorney-Holman & Stern ABSTRACT: A rotary screw machine in which theopenings for charging and discharging a gaseous working medium arelocated in the casing at both faces of the screws, and in which, in eachportion of the casing adjacent to the like faces of the screws at acertain distance from the opening provided in this portion of thecasing, a groove is provided along the line of engagement of the teethof the screws and facing the adjacent faces of the screws. One end ofthis groove is located at the dedendum circle of the teeth of the femalescrew while the other end of the groove is located beyond the addendumcircle of the teeth of this screw.

I /III PATENTEU UCT 5l97l SHEET 2 [1F 2 3,610,787

ROTARY SCREW MACHINE The present invention relates to rotary screwmachines, having male and female intermeshing rotary screws. Providedbetween the teeth of the screws and the machine casing are chambers intowhich a gaseous medium is admitted. If a torque is applied to one of thescrews these screws start to rotate and the machine compresses saidmedium functioning as a compressor.

If the gaseous medium is forced under pressure into the said chambers,the screws start to rotate and in this case the machine can be utilizedas a motor.

The present invention can be most effectively used, when the profile ofeach tooth of the male screw follows an elliptical, cycloidal or othercurve, whose shape is similar to that of said curves, while the profileof each tooth of the female screw follows a curve enveloping the curvesformed by the point of the tooth profile of the male screw during therotation thereof (such a profile is described in the USSR Inventor'sCertificate No. 125860, cl.27 c 3/01, 1960).

The known rotary screw machines have two openings for charging andremoval of the gaseous medium. One of these openings is usually locatedon the low-pressure side in the lower portion of the casing, while theother opening is located on the high-pressure, side in the upper portionof the casing. During the rotation of the screws closed chambers areformed on the low-pressure side and high-pressure side of the machine.

The closed chambers on the low-pressure 'side of the machine are formedbetween the rear flank of the tooth of the male screw and the front sideof the tooth of the female screw and the end wall of the casing. Thebeginning of their formation coincides with the initial moment ofengagement of the screws. In the course of further rotation of thescrews the volume of this chamber increases and reaches a maximum valuein the position of complete engagement of the screws. As a result, avacuum is formed within the closed chamber, and due to this fact a clampor shock wave occurs at the moment of communication of the chamber withthe high-pressure zone of the machine. This phenomenon causes theincreases of the noise level of the rotary screw machine and alsoresults in energy losses.

The closed chambers on the high-pressure side of the machine are formedbetween the front side of the tooth of the male screw, the rear flank ofthe tooth of the female screw and the end wall of the casing. Thebeginning of their formation coincides with the moment when thecontacting tooth of the male screw faces the axis of rotation of thefemale screw. During further rotation of the screws the size of thischamber decreases and disappears when the screws disengage.

As a result, an overpressure of the working medium in the closed chambertakes place and this is accompanied by the losses of the energy consumedfor the compression as well as by the claps or shock waves createdduring the communication of the closed chambers with the low-pressurezone of the machine, therefore, the noise level of the screw-rotormachine increases.

In order to reduce an adverse effect of the closed chambers the knownrotary screw machines are provided with grooves in the faces of the malescrews, one end of these grooves communicating with the lateral surfaceof the tooth. The other end of each groove in the course of rotation ofthe screws passes by the values built into the casing and communicatingthe closed chamber with the high-pressure zone (for example, see theU.S.A. Pat. Specification No. 2,578,196).

In the process of making the known machines of the abovementioned typeand during their maintenance there are difficulties associated withplacing the valves in the machine casing and with controlling the stateof the valves during their maintenance. Furthermore, these valvesdecrease the rate of changing the pressure within the closed chambersunproportionally to the change of this rate due to the fact that theirarea of passage is invariable.

The main object of the invention is to provide such a rotary screwmachine in which the closed chambers after their formation during therotation of the screws constantly communicate with the zone of such apressure whose value is close to the value of pressure within the closedchamber.

According to the invention this object is achieved by providing a groovein each portion of the casing adjoining the like faces of the teeth atsome distance from the opening made in this portion of the casing, saidgroove being located along the line of engagement of the teeth of thescrews and facing the adjacent faces of the screws. In this case one endof the groove is located at the dedendum circle of the teeth of thefemale screw, while the other end of the groove is located beyond theaddendum circle of the teeth of this screw.

Such an embodiment of the rotary screw machine makes it possible toprovide for the same effect which is obtained by means of the previouslyknown valves. In this case, however, the design of the machine isessentially simplified, while the reliability thereof is increased.

In order to reduce the rate of changing the pressure within the formedclosed chambers on the low-pressure side proportionally to the change ofthis rate, it is expedient to make a groove in said side of the face ofeach tooth of one screw, particularly, the male one, at the part of thetooth profile, located backwards as viewed in the direction of rotationof the screw, said groove communicating the middle portion of the toothprofile with a portion of this profile at the tooth root.

In order to reduce the rate of changing the pressure within the formedclosed chambers on the high-pressure side proportionally to this rate itis expedient to make a groove in said side of the face of each tooth ofone screw, particularly, the male one, at the part of the tooth profilelocated in front as viewed in the direction of rotation of the screw,said groove communicating the middle portion of the tooth profile with aportion of this profile at the tooth root.

The basic advantage of the invention consists in that the noise level ofthe compressor or pump is reduced approximately by 20 percent while theenergy losses are correspondingly reduced.

Given below is a detailed description of an embodiment of the rotaryscrew compressor or pump, according to the invention, with reference tothe accompanying drawings, in which:

FIG. 1 illustrates a longitudinal section of the rotary scre machineaccording to the invention;

FIG. 2 is a section taken along the line II-II of FIG. 1;

FIG. 3 is a section taken along the line III-III of FIG. 1;

FIG. 4 is a section taken along the line IVIV of FIG. 2;

FIG. 5 is a section taken along the line V-V of FIG. 3.

The rotary screw machine comprises a male screw 1 (FIG. 1) and a femalescrew 2 (FIG. 2) mounted within the casing 3 and engaging the screw 1.Provided in the lower portion of the casing on the low-pressure side isa branch 4, while the upper portion of the casing on the high-pressureside is provided with a branch 5. The branches 4 and 5 are intended forcharging and discharging a gaseous working medium and communicate withthe chambers formed between the teeth of the screws and the casing 3 ofthe machine through the opening 6 (FIGS. 1 and 2) and opening 7 (FIGS. 1and 3) respectively. The contact of the teeth 8 of the male screw 1 andthe teeth 9 of the female screw 2 at the like faces of the screws iseffected along the lines of engagement AB and NB (FIG. 2) and along thelines of engagement CD and C'D' &(FIG. 3) respectively. Provided in thecasing 3 at each of said openings at some distance therefrom along thelines AB and C'D' of engagement are a groove 10 (FIG. 2) and a groove 11(FIG. 3) respectively, facing the adjacent respective faces of thescrews 1 and 2, as shown in FIGS. 2, 3, 4 and 5. In this case one end ofeach groove is located at the dedendum circle of the teeth 9 of thefemale screw 2, whereas the other end is located beyond the addendumcircle of the teeth of this screw.

Owing to the fact that the closed chambers between the contacting teeth8 and 9 of the screws 1 and 2 are formed along the grooves 10 and 11,these grooves provide for constant communication of said closed chamberswith the openings 6 and 7 respectively.

Such a design makes it possible to eliminate a rapid change of pressurewithin these chambers or a significant pressure drop of the workingmedium within these chambers and in the zones adjoining the branches 4and respectively.

Noisy exhaust of the working medium from these chambers as well as anyclaps or shock waves are eliminated. The energy losses of the compressorare reduced.

it is understood that the grooves 9 and 10 may even have rectilinearsections, however, these sections should be tangential to the line ofengagement.

Owing to the fact that the closed chambers feature a variable volume itis expedient to increase the cross section of the passage through whichthey communicate with one of said zones at the moments, when the rate ofchanging their volume is maximum.

To solve this problem the face of each tooth 8 of the male screw 1 onthe low-pressure side (at the opening 6) and at the portion of the toothprofile which is backwards as viewed in the direction of rotation of thescrew 1 is provided with a groove 12 (FIGS. 1, 2, 3) communicating themiddle part of the profile of the tooth 8 with a section of this profileat this tooth root. In these places the rate of changing the volume isthe highest, therefore, the groove 12 will communicate the closedchamber with the low-pressure zone at the moments of the maximum rate ofchanging of Said volume.

On the high-pressure side (at the opening 7) the above problem is solvedwith the help of a groove 13 made on the face of each tooth 8 of themale screw 1 on said side, the groove 13 being located at that portionof the profile which is forward as viewed in the direction of rotationof the screw 1. This groove communicates the middle part of the profileof the tooth 8 with the section of this profile at the root of the tooth8. In order to simplify the process of manufacture of the grooves 12 and13 it is expedient to make them arc-shaped.

It is clear that the grooves are preferably made in the male screwhaving convex (wide) teeth.

We claim:

1. A rotary screw machine comprising a casing having an inlet branch andan outlet branch for a gaseous working medium, male and female screwslocated inside said casing and being in engagement, an inlet openingprovided in said casing at the first like faces of said screws, anoutlet opening within said casing at the other like faces of saidscrews, a groove in each portion of said casing adjacent to said firstlike faces and to the second like faces of said screws, said groovebeing located along the line of engagement of the teeth of the screws at.a distance from the corresponding opening and facing the adjacent facesof said screws, one end of this groove being located at the dedendumcircle of the teeth of said female screw and the other end of thisgroove being located beyond the addendum circle of said teeth of thisscrew.

2. A rotary screw machine according to claim 1 in which at thelow-pressure side of the face of each tooth of one of said screws atthat portion of the profile of this tooth which is backward as viewed inthe direction of rotation of said screw, a groove is provided connectingthe middle portion of said profile of said tooth with a section of thisprofile at the root of said tooth.

3. A rotary screw machine according to claim 1 in which at thehigh-pressure side on the face of each tooth of one of said screws atthat portion of the profile of said tooth which is forward as viewed inthe direction of rotation of said screw, a groove is provided connectingthe middle portion of said profile of said tooth with a section of thisprofile at the root of said tooth.

1. A rotary screw machine comprising a casing having an inlet branch andan outlet branch for a gaseous working medium, male and female screwslocated inside said casing and being in engagement, an inlet openingprovided in said casing at the first like faces of said screws, anoutlet opening within said casing at the other like faces of saidscrews, a groove in each portion of said casing adjacent to said firstlike faces and to the second like faces of said screws, said groovebeing located along the line of engagement of the teeth of the screws ata distance from the corresponding opening and facing the adjacent facesof said screws, one end of this groove being located at the dedendumcircle of the teeth of said female screw and the other end of thisgroove being located beyond the addendum circle of said teeth of thisscrew.
 2. A rotary screw machine according to claim 1 in which at thelow-pressure side of the face of each tooth of one of said screws atthat portion of the profile of this tooth which is backward as viewed inthe direction of rotation of said screw, a groove is provided connectingthe middle portion of said profile of said tooth with a section of thisprofile at the root of said tooth.
 3. A rotary screw machine accordingto claim 1 in which at the high-pressure side on the face of each toothof one of said screws at that portion of the profile of said tooth whichis forward as viewed in the direction of rotation of said screw, agroove is provided connecting the middle portion of said profile of saidtooth with a section of this profile at the root of said tooth.